Heretofore, as an input/output protective element for semiconductor devices, a PN junction diode using a PN junction formed by a P type high concentration diffusion region in an anode region and an N type high concentration diffusion region in a cathode region on both sides thereof to a low concentration N type semiconductor substrate has been known (for example, refer to JP-A-Hei 8 (1996)-316480).
Further, as an input/output protective element for semiconductor devices, a semiconductor device has been known so far in which a high voltage diode as a protective element is formed over a semiconductor substrate identical with that of a high voltage NLDMOS which is a device to be protected, and a P type low concentration diffusion region of the high voltage diode is formed simultaneously with a P type low concentration diffusion region as a well of a high voltage NLDMOS and a P type high concentration diffusion region of the high voltage diode is formed simultaneously with a P type high concentration diffusion region for a well feed region of the NLDMOS, respectively (for example, refer to JP-A-2000-114266).